Electric discharge device



April 18, 1950 5, POWER 2,504,581

ELECTRIC nxscumcn: DEVICE- Filed April 7, 1947 InvenTo r: Er-nesTBenJcminPower,

3 W 1 His ATTorne y.

Patented Apr. 18', 1950 ELECTRIC DISCHARGE DEVICE Ernest Benjamin Power,Kenton, England, assignor to General Electric Company, a comratlon oiNew York Application April 7, 1947, Serial No. 739,831 In Great BritainApril 17, 1946 6 Claims.

My invention relates'to electric jdiscliarge devices, and moreparticularly to high-pressure mercury vapor lamps of the high-pressuretype This disadvantage has been encountered where the lamps are operatedon direct current. As a result of this wandering of the cathode spot thecenter of the light source consequently moves and the arc length varies.In accordance with my invention described hereinafter I provide a newand improved high-pressure mercury vapor lamp wherein the abovedescribed disadvantage is obviated.

An object of my invention is to provide a new and improved electricdischarge device.

Another object of my invention is to provide a new and improvedhigh-pressure mercury vapor lamp of the type in which the distancebetween are supporting surfaces of the anode and cathode is less thanthe distance from either surface to the enclosing envelope.

It is a further object of my invention to provide new and improvedelectrode structures for high-pressure mercury vapor lamps.

Generally speaking, in accordance with my invention I provide animproved high-pressure mercury vapor electric discharge lamp wherein thearc length remains substantially constant during normal operationrendering it highly satisfactory for projection purposes. An anode and acathode each constructed of a solid block of refractory metal arepositioned on and supported by relatively heavy lead-in conductors orrods and these electrode structures are located transverse to theprincipal axes of the lead-in rods. For example, where the lamp isintended for vertical operation, the lead-in rods are vertical and theprincipal axes of the members constituting the anode and cathode arepositioned horizontally. A further feature relates to the manner inwhich activating material is positioned and supplied to the arcsupporting surface of the cathode, a recess being provided in thelead-1n rod which supports the cathode and means is provided forsupporting the activating material in this recess but which also permitsegress of activating material to the are supporting surface.

For a better understanding of my invention reference may be had to thefollowing description taken in connection with the accompanying drawingand its scope will be pointed out in the ap pended claims. Fig. 1 is avertical view of one lamp constructed in accordance with my invention,and Fig. 2 is a much enlarged view of the cathode structure and thesupporting lead-in rod which houses the activating material.

Referring now to Fig. 1 I have there illustrated my invention as appliedto an electric discharge device, such as a high-pressure mercury vaporlamp I. This lamp is of the type intended for operation in which thepressure of the mercury vapor is one atmosphere or more and is of thetype furnishing a compact source of light.

' More specifically it may be stated that the discharge lamp is of thehigh-pressure type in which the arc length or the distance between arcsupporting surfaces of the cooperating electrodes is less than thedistance from either surface to th vitreous envelope 2. I provide a pairof lead-in conductors or rods 3 and I, which are preferably arranged ina vertical position and which are sealed to tabulations 5 and 6 by anysuitable sealing structures 1 and 8, respectively, providing at thelower extremities thereof externally accessible contacts 8 and it. Thesealing structures 1 and 8 may be of the type disclosed and claimed inUnited States Patent No. 2,400,946, granted May 28, 1946 upon anapplication of E. H. Nelson et al., and which is assigned to theassignee of the present invention.

The lead-in rods 3 and l are constructed of refractory metal such astungsten and in one embodiment of my invention comprise tungsten rodshaving a diameter of approximately 3 mm.

On one of the lead-in rods I position an anode l I,

preferably constructed of a single block of refractory metal such astungsten, and which is arranged to have its principal axis transverse orperpendicular to the axis of the lead-in rod 3.

Anode H is provided with an arc supporting surface 12 preferably arcuatein shape. In one form the anode ll may have a substantiallysemispherical shape with the convex are supporting surface l2 facing thecathode structure described immediately hereinafter.

The details of the cathode structure may be more fully appreciated byreferring to the much enlarged view thereof shown in Fig. 2. The cathodestructure 13 is preferably constructed of a single cylindrical piece orblock of refractory metal, such as tungsten, and is provided with a basepart M which is joined to or welded to the lead-in rod 4. At oneextremity of the cathode ii I provide a bulbous part l affording an aresupporting surface Hi to face the arc supporting surface I! of anode II,and which is connected to base part H by a contracted or neck section 41to limit or minimize the flow of heat from the bulbous part I5 to theother parts of the electrode structure or assembly, thereby serving tomaintain the temperature of the cathode during normal operation at orabove a predetermined value, whereas the anode H is substantially moremassive than the cathode I3 so that it effectively dissipates theexcessive heat thereat during operation. The contracted section i'l maybe formed by a grinding operation and the bulbous part i5 need not besymmetrical and may have a slightly flattened appearance as shown inFig. 2 of the drawing.

In order to supply activating material to the cathode I provide a recess18 in the supporting rod 4 for the cathode, and which may be formed bygrinding away a section of the rod 4. Within the recess 18 I positionactivating material l9 which may comprise a composite body of oxides ofthe alkaline earth metals, or mixtures thereof, and which may be held ina compact form by means of a winding of tungsten wire 20 which by virtueof the small spacing between the turns thereof permits egress ofactivating material through a second spiral or winding of tungsten wire2| whichretains the activating material I! in the recess It.

In one form of lamp constructed in accordance with my invention thespacing between the arc supporting surfaces l2 and I6 is preferablywithin the range of 5 to 10 mm. and the vertical and horizontaldimensions of the bulbous part ii are respectively 1 mm. and 1 mm. foran are dis: charge path of 6 mm. The cathode I3 is formed of a 1.5 mm.tungsten rod Joined to the associated 3 mm.'tungsten rod 4 by arcwelding. The length of the cathode structure I3 to the point where it isJoined to the rod 4 may be approximately 3.5 mm., and the contracted orneck part I] may be 0.5 mm. in diameter having a length of from 0.75 to1 mm.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric discharge device of the type employing an ionizablemedium and for operation on direct current, the combination comprisingan envelope and a pair of electrodes positioned therein and having aresupporting surfaces thereof spaced a distance less than the distancefrom either surface to the envelope, one of said electrodes serving asan anode and constructed of a block of refractory metal substantiallymore massive than the other electrode and having its principal axistransverse to and supported by a lead-in conductor, and the said otherelectrode having a part thereof transverse to and of smaller crosssectional area than its supporting lead-in conductor and having abulbous part serving as a cathode and connected to a base part by acontracted section to limit the flow of heat to the associated lead-inconductor.

2. In an electric discharge lamp of the highpressure type for directcurrent operation, the combination comprising an envelope and includingan anode and a cathode, said anode comprising a block of refractorymetal substantially more massive than the cathode and having'a convexarc supporting surface and said cathode comprising a similar body ofrefractory metal provided with a bulbous part having an arc supportingsurface and connected to a base part, by a contracted section having a.smaller crosssectional area than said base part for limiting the flow ofheat from the bulbous part.

3. In an electric discharge lampof the highpressure mercury vapor typefor direct current operation, the combination comprising an envelope, apair of vertical lead-in rods, and an anode and cathode each constructedof a solid block of refractory metal, said anode being substantiallymore massive than said cathode and of substantially cylindrical shapeprovided with a convex face for supporting an arc discharge, and

said cathode having a base part and a bulbous arc supporting partconnected to the base part by a contracted section for limiting the flowof heat to the base part, the lead-in rod supporting said anode being ofsmaller cross-sectional area than said anode and the lead-in rodsupporting said cathode being of larger diameter than said base part.

4. In an electric discharge lamp of the high pressure mercury vapor typefor direct current operation, the combination comprising an envelope, apair of vertical lead-in rods, and a horizontally positioned anode andcathode supp rted respectively by said rods and each constructed of asolid block of tungsten, said anode being substantially more massivethan said cathode and of substantially cylindrical shape having a convexare supporting surface and said cathode having a bulbous part serving asan arc supporting surface and connected to a base part by a contractedsection for maintaining the temperature of the bulbous part at or abovea predetermined value during operation of the lamp, the lead-in rodsupporting said anode being of smaller crosssectional area than saidanode and the lead-in rod supporting said cathode being of largerdiameter than said base part.

5. In an electric discharge device of the type employing an ionizablemedium and for direct current operation, the combination comprising anenvelope, a pair of lead-in rods of refractory metal, and an anode andcathode supported by said rods, said anode being substantially moremassive than said cathode, said cathode comprising a body of refractorymetal provided with a bulbous part having an are supporting surface andconnected to a base part by a contracted section for limiting the flowof heat from the bulbous part, a recess in the lead-in rod supportingsaid cathode, activating material in said recess, and means forsupporting said activating extending transversely thereof toward eachother, said anode being substantially more massive than said cathode,the end of said cathode nearer said anode being separated from theremainder of the cathode by a neck portion of materially reduced 5cross-sectional area to maintain the said end of the cathode. duringoperation, at a higher temperature than in the absence of the said neckportion and thereby prevent wandering of the are from the surface of thecathode which faces 1.

said anode.

ERNEST BENJAMIN POWER. v

REFERENCES CITED The following references are of record in the file ofthis patent! UNITED STATES PATENTS Great Britain Feb. 19, 1942

